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Math Help - CHemistry Help

  1. #1
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    CHemistry Help


    Identifying an Unknown


    -you will be given a solid that can be either: NaHCO3, KHCO3, or CsHCO3
    -your goal is to identify the unknown solid based on the following chemical reaction:
    -remember that if you combine a carbonate with excess of sulfuric acid CO2 will be on of the products.

    M = Na, K or Cs

    complete and balance:
    MHCO3 (ac) + H2SO4 (ac) --> CO2 (g) +

    task: develop a procedure to identify the unknown based on the chemical reaction

    im pulling my hair here, i have know idea how to carry out this experiment!! im not good at labs grrr
    help please

    oh yeah these are some guide questions but somehow i dont feel guided by them:

    * How many grams of unknown should u use?
    * how many mL of sulfuric acid are required for it to react with the unknown
    * how would u determine the mass of CO2 generated?

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  2. #2
    Super Member
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    Oct 2007
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    London / Cambridge
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    Quote Originally Posted by NeedHelp18 View Post

    Identifying an Unknown


    -you will be given a solid that can be either: NaHCO3, KHCO3, or CsHCO3
    -your goal is to identify the unknown solid based on the following chemical reaction:
    -remember that if you combine a carbonate with excess of sulfuric acid CO2 will be on of the products.

    M = Na, K or Cs

    complete and balance:
    MHCO3 (ac) + H2SO4 (ac) --> CO2 (g) +

    task: develop a procedure to identify the unknown based on the chemical reaction

    im pulling my hair here, i have know idea how to carry out this experiment!! im not good at labs grrr
    help please

    oh yeah these are some guide questions but somehow i dont feel guided by them:

    * How many grams of unknown should u use?
    * how many mL of sulfuric acid are required for it to react with the unknown
    * how would u determine the mass of CO2 generated?

    MHCO3 (ac) + H2SO4 (ac) --> CO2 (g) + H2O + M SO4

    I believe the experiment should go something like this:

    - Assume your unknown is the lightest (as is has the lowest grams per moles compared to the others). NaHCO3 has a relative mass of 84 grams per mole, so if your using say 3 grams of the unknown substance you will need at least 3/84 moles of H2SO4 for a complete reaction. I believe you should use a tiny bit more to ensure that you will get a complete reaction regardless of what the unknown is.

    - I guess you either do the experiment on a scale or weight the beaker your doing the test in before and after the experiment to determine the mass different and hence the mass of the CO2 given off. once you know the mass of the CO2 you can determine the number of moles of CO2 and therefore the number of moles of the unknown substance you had. you know the mass of the substance you used so you will be able to work out its relative mass and hence determine what it is.

    Bobak
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